Surface treatment of workpieces



April 1969 B. F. BLUNDELL 3,435,565

5 SURFACE TREATMENT OF WORKPIECES Filed Feb. 2, 1967 Sheet of 4 Filed Feb. 2, 1967 April 1, 1959 B. F. BLUNDELL 3,435,565

SURFACE TREATMENT OF' WORKPIECES Sheet 2 of 4 April 1, 1969 a. F. BLUNDELL 5,5

SURFACE TREATMENT OF WOBKPIEOES Filed Feb. 2/1967 Sheet 3 pm Y V J Aprfl 1, 1969 B. F. BLUNIIJELL 3,435,565

SURFACE TREATMENT OF WORKPIEQES Filed Feb. 2, 1967' v Sheet 4 of 4 F "5 :1". ::::::J t: 111:1?)

l l\ 8 70 I El United States Patent US. Cl. 51--313 3 Claims ABSTRACT OF THE DISCLOSURE Very rapid abrasive finishing treatment of workpieces is obtained by using centrifugal force to cause the mass of abrasive media in which the workpieces are immersed to assume a toroidal form, with individual particles circulating helically around the toroid. In the preferred forms of apparatus, a dished platform rotates about a vertical axis within the lower end of a stationary vertical walled tub of polygonal cross-section. The workpieces may be loosely mixed with the media and may be extracted after treatment by lowering a sieving basket into the circulating mass. Alternatively the workpieces may be secured to stationary or moving fixtures.

This invention provides a novel method of effecting abrasive surface treatment of workpieces, and a 'novel machine for carrying out the method.

The term surface treatment includes such operations as de-burring, radiusing and polishing of workpieces, whether of metal or other materials, and is commonly carried out by burying the workpieces in a mass of small pieces, or chips, of abrasive material, such as alumina or other minerals or ceramics, commonly known as media.

The media is usually kept wetted with liquid, which may include soap or other lubricants. The whole mass is usually contained in a tub or other container which is either rotated to cause the contents to tumble, or is vibrated in order to produce the required relative movement between the workpieces and the abrasive medium.

The present invention provides a method and apparatus for effecting surface treatments similar in character to those obtained with the known tumbling barrels and vibratory finishing machines, but effecting them very much more rapidly, so that the time required to effect the treatment is correspondingly reduced.

In accordance with the method of the invention the mass of abrasive medium is maintained in motion by imparting to it a rapid rotation about a substantially vertical axis, so that under the influence of centrifugal force the medium .flows outwardly, this outwardly flowing stream being then returned inwardly above the outwardly flowing material, so that the mass assumes and maintains a toroidal form, with individual particles of the mass traveling helically around the toroid. As in the known types of finishing apparatus, the workpieces may either be loose and mixed with the abrasive media, or they may be secured on fixtures (which may hold them stationary, or may impart any desired degree of movement to the workpieces) the circulating media flowing over the workpieces.

Several alternative forms of apparatus in accordance with the invention are described below by way of example with reference to the accompanying drawings. In these drawings:

FIGURE 1 represents a side view, partly in section of one form of the apparatus of the invention;

FIGURE 2 is an enlarged sectional view of a detail;

FIGURE 3 is another detail sectional view, showing 3,435,565 Patented Apr. 1, 1969 ICC an indication of the paths of movement of the circulating material;

FIGURES 4 and 5 are views corresponding to FIG- URE 2, showing modifications;

FIGURE 6 represents a side view, partly in section, of another form of apparatus in accordance with the invention; and

FIGURE 7 is a plan view of the apparatus of FIG- URE 6.

Referring first to FIGURE 1, a stationary base 1 supports a driving motor 2 which, through a V belt 3 and a worm reduction gearing unit 4, drives a vertical shaft 5, the motor being slideably mounted on the base so that it can be moved to adjust the belt tension. Secured to the upper end of the shaft 5 is a dished platform or bowl 6, having a lining 7 of rubber or similar material. This bowl fits 'within and substantilaly closes the lower end of a stationary tub 8, supported from the base 1. The tub has in general the form of an open-ended vertical tube of octagonal cross-section, but its lower end is circular to fit closely around the periphery of the bowl 6, a conically chamfered portion 9 at the lower end of the tub having the same inclination to the vertical as the outer portion of the bowl, so that the internal surfaces of bowl and tub merge smoothly together. The tub 8 is provided with a lining 10 of rubber or similar material, which may be bonded to the tub wall, but is preferably constituted by a separately formed sleeve inserted into and secured to the tub, thereby facilitating replacement of the lining when it becomes worn.

Within the upper part of the tub 8 and extending around at least a major part of its periphery is a perforated pipe 11, for discharging liquid onto the contents of the tub. Liquid is supplied to sprinkler pipe 11 through a pipe 12 by a pump 13 immersed in a tank 14. As shown, liquid escaping from the tub around the periphery of rotating bowl 6 is collected in a chamber 15 and drains back through a channel 16 into the tank 14, which may be provided with baffles and/ or filters (not shown) to remove suspended solid matter from the liquid before it reaches the intake of pump 13. Alternatively, of course, fresh liquid may be supplied continuously to sprinkler pipe 11, the liquid collected in chamber 15 being discharged to waste, or to separate recovery plant.

As best seen from FIGURE 2, which is an enlarged view of part of the machine of FIGURE 1, the peripheral edge of the rotating bowl 6 is beveled on its outer face, the extreme edge of the bowl lining 7 lying very close to the tub lining 10, but spaced from it by a small gap to avoid excessive friction. This gap is sealed against the passage of anything but liquids and very finely divided solids by a brush 16, secured to the bevelled face of the bowl and extending completely around the bowl. The brush consists of bristles of nylon or other suitable material, secured at their roots in a suitable clamp and bearing at their tips against the downward extension of the stationary tub wall which forms the chamber 15.

Extending upwardly along the axis of the tub is a shaft 17, which is connected at its lower end to the shaft 5. Surrounding shaft 17 is a tubular shaft 18 of square crosssection, upper and lower plain bearings 19, 20 being interposed between shafts 17 and 18 and the upper ends of the shafts being supported by a bearing 21 carried by a stationary frame 22. A clutch 23, operated by a lever 24, allows the outer, square shaft 18 to be disengaged from, or coupled to, shaft 17, which rotates with the bowl 6 and the driving shaft 5. A band brake 25, operated by a lever 26, allows the outer shaft 18 to be brought to rest after disengagement of clutch 23. Tubular shaft 18 is in turn surrounded by a sleeve 27, having at its upper and lower ends square openings which fit with clearance around the square shaft 18, so that the sleeve will rotate with shaft 18, but can be moved upwardly and downwardly along the shaft. Connected to the upper end of sleeve 27 by a bearing 28 is a non-rotating arm 29, which is slidably mounted on a vertical column 30 and can be moved upwards and downwards by an hydraulic cylinder 31. Secured to the lower end of sleeve 27 is an opentopped circular basket 32, whose side Wall at least is formed of wire mesh or perforated sheet metal, or otherwise provided with numerous apertures.

In operating the machine of FIGURE 1, the tub 8 is charged with a suitable quantity of solid processing media, such as stone fragments or ceramic or plastic chips of the character used in tumbling barrels and vibratory finishing machines, and the workpieces to be treated are added. With basket 32 (which is shown in an intermediate position) raised well clear of the charge by operation of cylinder 31, motor 2 is energised to drive shaft 5 and thus rotate bowl 6 about its vertical axis. The charge of media and workpieces is by centrifugal force thrown outwardly and upwardly against the stationary wall of the tube 8, and thence returns inwardly and downwardly above and inside the outwardly flowing material. The charge thus assumes a toroidal form, with individual elements of the charge moving along helical paths around the toroid, as suggested by the broken lines and arrows in FIGURE 3. The height reached by the charge before the retardation effected by the stationary wall is sufficient to cause it to fall back on to the rotating bowl, depends upon the speed of rotation of the bowl. FIGURE 6 shows by way of example two of the forms which the charge may assume, the toroid whose cross section is indicated by the arrows 33, 34 corresponding to a relatively low speed of rotation and that indicated by the arrows 35, 36 corresponding to a relatively high speed. For a tub measuring 2 feet in diameter, speeds of rotation of the bowl lying in the range from 150 to 250 revolutions per minute are suitable, proportionately higher speeds being used for smaller tubs and lower speeds for larger tubs.

During the whole period of the treatment, the charge is kept moistened with liquid supplied through the sprinkler tube 11, this liquid, together with finely divided solid matter produced by the abrasive interaction of the media and workpieces, draining out of the tub into the chamber through the annular gap between bowl and tub wall. The liquid used, and also the solid media used, are selected to accord with the nature of the workpieces to be treated and the character of the finishing operation to be performed upon them. In general, media and liquids suitable for performing a given finishing operation in tumbling barrels and vibratory finishing machines can be used to perform the same operation in the machines of the present invention, but in the latter the operation is performed very much more rapidly, so that the treatment time is greatly reduced.

The circulation of the mass of media and workpieces in the manner described is assisted by the shaping of the bowl so that the mass is thrown upwardly as well as outwardly against the wall of the tub. The outer part of the surface of the bowl should slope upwardly and outwardly at an angle to the horizontal of at least 15 preferably to 50. While the tub wall may be circular in plan view, the establishment of the desired circulation is assisted by using a polygonal tub, such as the octagonal tub shown, as this more quickly reduces the rotational velocity of the mass.

When the processing of a batch of workpieces has been completed, the workpieces can be extracted from the tub, without removing the media, by means of the basket 32. The clutch 23 may be operated to connect the shafts 17 and 18, so that the basket rotates at the same speed as the bowl 6, the cylinder 31 being then operated to lower the basket into the bowl. The diameter of the basket is greater than the internal diameter of the toroidal mass, so that the material returning inwardly and downwardly is received in the basket. The openings in the wall of the basket have dimensions several times those of the individual chips (or pieces of media), so that the media continues to circulate as before, but the openings are too small to allow the passage of the workpieces, which are consequently retained in the basket. After a short period of immersion in the mass, the basket is raised clear of the mass, rotation being continued so that most of the chips which have been lifted with the basket will be discharged by centrifugal force. Any risk that workpieces will be thrown out over the rim of the basket is avoided by the provision of a retaining lip, as indicated at 37. The basket is then brought to rest by disengaging clutch 23 and operating brake 25 and the workpieces are removed from the basket. This sequence of operations is repeated as often as is necessary to extract all the workpieces of the batch, after which the apparatus is ready to receive a fresh batch of workpieces.

Instead of positively driving the basket through clutch 23, the basket may simply be left free to rotate about the axis of shaft 17. When the basket is lowered into engagement with the circulating mass, it is rotated by the action of this mass and on reaching the bottom of its travel it engages the bowl 6 and rotates with the latter. When again raised clear of the mass, it quickly loses speed, this manner of operation, which is satisfactory in certain cases at least, allows the omission from the apparatus of shaft 18, clutch 23 and brake 25.

It may be desirable when the basket is lowered into the circulating mass, to introduce into the tub a baflle or deflector for checking the rotational movement of the mass and diverting it inwardly, thereby ensuring that the whole of the mass flows through the basket and that complete recovery of the workpieces is effected. As shown in FIGURE 1, a deflector blade 38 is so mounted on arm 29 that when the basket is raised, the blade 38 will be clear of the circulating mass, while When the basket is lowered, the blade will project into the mass between the wall of the tub and the basket. Instead of introducing the deflector blade into the tub from above, as shown, a part of the wall of the tub may be formed as a hinged panel, which can be swung inwards to form a deflector when required, or a deflector plate can be mounted for substantially radial movement through a slot in the wall of the tub.

To facilitate discharge of the media from the tub when renewal or replacement is required, the tub wall is formed with an opening normally closed by a door 39, which can be opened to allow the media to escape under the influence of the centrifugal force generated by rotation of the bowl. The door may be hinged to open inwardly, so that assists in deflecting the media through the opening and may be constituted by one wall of a chute or tube for guiding the media as it leaves the tub. Such a door may also be used for discharging the whole contents of the tub, separation of the workpieces from the media being effected after discharge by any convenient means.

The sealing of the gap between the edge of the rotating bowl and the surrounding wall of the tub may be effected in many ways other than that shown in FIGURES 1 and 2. In the construction shOWn in FIGURE 3, the rubber or like lining 10 of the tub wall terminates some distance above the top of the bowl 6 and the rubber or like lining 7 of the bowl is extended some distance beyond the rigid part of the bowl to form a flap 40, which bears against the downward extension 15 of the tub wall and forms a smooth continuation of the lining 8, with which it makes a bevelled joint as shown. In the construction of FIGURE 4, the reverse arrangement is employed, the bowl lining 7 terminating some distance inside the edge of the rigid bowl 6 while the tub lining 10 is formed with a projecting flap 41 which engages the marginal part of the bowl and makes a bevelled joint with the bowl lining. FIGURE 5 shows yet another possible sealing arrangement, the projecting margin 42 of the bowl lining 7 making a close fit against the lower edge of the tub lining 10. FIGURE 5 also shows one of the possible variations in the shape of the bowl, which in this case has its outer portion spherically dished (instead of being conically sloped at a constant angle, as in FIGURES 1 to 4) the radius of curvature being so chosen that the outer part of the bowl has the required inclination to the horizontal.

Instead of mixing the workpieces with the media so that they partake in the toroidally helical circulation, the workpieces may be secured to fixtures, the media being caused to circulate over the workpieces. Such fixtures may be mounted on the wall of the tub, or other fixed part, but are preferably so mounted that they can be raised out of the tub to facilitate loading and unloading. Thus, in

the apparatus of FIGURE 1, fixtures for holding workpieces may be mounted on the arm 29, or some part which moves with it, such as the sleeve 27. The fixtures may be held stationary while the workpieces are under treatment, or they may be permitted or caused to rotate during the treatment.

The machine shown in FIGURES 6 and 7 again comprise a bowl 6 with a rubber or like lining 7 fitting within the lower end of a stationary octagonal tub 8 with a rubber or like lining 10, the bowl being in this case mounted directly on the shaft of an hydraulic motor 43. An upward extension 44 of the motor shaft is supported at its upper end in a bearing 45 carried by a fixed frame 46. Shaft extension 44 serves to locate on the axis of the tub a sleeve 47, which is slidable on the shaft and carries at its upper end a clamp 48. Outside the tub is a vertical column 49, which is capable of rotation about its own axis and can be raised and lowered by means of a screw jack 50, driven by a motor 51. At its upper end, column 49 carries a cross bar 52, which terminates at each end in an arcuate plate 53 adapted to be gripped by the clamp 48. Adjacent each end, the cross bar 52 carries a spindle assembly 54, which is adjustable along the length of the cross arm and includes a vertical work holding spindle 55 and a motor 56 for rotating the spindle about its axis.

A workpiece to be treated is secured to the spindle 55 of the assembly 54 which is outside the tub. Jack 50 is operated to lift column 49 and the parts connected to it. Clamp 48 is released, cross arm 52 is turned through approximately 180", and the clamp is retightened to grip plate 53 and secure the cross arm. Jack 50 is then operated to lower the workpiece into the circulating mass of media in the tub. The position of the workpiece in the tub can be varied, to secure the desired finishing action, by adjusting the position of the assembl 54 along bar 52 and the position at which plate 53 is gripped by clamp 48. During treatment the workpiece may be continuously or intermittently rotated by operating motor 56. While one workpiece is under treatment, the assembly 54 which is outside the tub, may have a workpiece which has already been treated removed and a fresh workpiece fitted.

While a number of alternative embodiments of the invention have been described above, a great many other modifications are possible, the possibilities mentioned below being intended by Way of further example only.

The tub walls, instead of being vertical as shown, may be incurved or otherwise shaped. Instead of being stationary, they may be rotated at a speed different from that of the platform, or in the reverse direction. However, vertical stationary walls have the advantage of simplicity and have been found in practice to give good results.

Instead of delivering liquid from above onto the material in the tub and allowing it to drain out through the gap between the rim of the platform and the tub walls, liquid may be forced upwardly into the tub through the said gap. The rotating platform may itself serve as the rotor of a pump for producing such liquid flow, a liquid reservoir being provided below the platform and pump vanes being carried on the underside of the platform. Apparatus in accordance with the invention can also be used to carry out dry finishing treatments; when so treating workpieces of some materials a substantial amount of powder may be produced and to allow this powder to escape the walls of the tub may be perforated.

I claim:

1. A method of finishing workpieces by immersing the workpieces in a mass of particulate abrasive media and causing relative movement between workpieces and media, characterised in that the media is maintained in movement by imparting to it a rapid rotation about a substantially vertical axis, so that under the influence of centrifugal force the media flows outwardly and upwardly, and by returning the media inwardly and downwardly above the outwardly flowing stream, so that the mass of media assumes a toroidal form with individual particles of the media travelling helically around the toroid.

2. A method in accordance with claim 1 in which the workpieces are loosely mixed with the media and partake in the helically toroidal circulating movement.

3. A method in accordance with claim 1 in which the workpieces are secured to fixtures and the media is caused to circulate past them.

References Cited UNITED STATES PATENTS 1,647,249 11/1927 Podzus 51163 3,392,925 7/1968 Moore 51-163 X 3,173,664 3/1965 Isaacson et al 51-163 X JAMES L. JONES, JR., Primary Examiner.

US. Cl. X.R. 

